Parvovirus B19 (B19V) infection causes human bone marrow failure by destroying the bone marrow resident erythroid progenitor cells (EPCs), which support autonomous replication of the virus. In patients with a high demand for erythrocyte production due to high levels of erythrocyte destruction (e.g., sickle-cell disease patients), acute B19V infection can cause transient aplastic crisis. In immunocompromised patients, persistent B19V infection may manifest as pure red-cell aplasia. In the fetus, B19V infection can cause hydrops fetalis, a severe form of anemia. B19V infection induces damage of EPCs, which results in the above bone marrow failures. B19V-infected EPCs undergo cell death with clear apoptotic features. This cell death is induced mainly by high expression of the non-structural 11kDa protein (11kDa) during infection, and involves a caspase cascade triggered by caspase-10. In the proposed research, we aim, firstly, to reveal the molecular mechanism underlying caspase-10- mediated apoptosis in response to 11kDa. To this end, we will determine which apoptotic pathway the extrinsic or the intrinsic activates the initiator caspase-10 during B19V infection-induced apoptosis. As both the apoptotic and anti-apoptotic pathways play key roles in erythropoiesis and the homeostasis of EPCs, we propose to identify the cellular proteins that interact 11kDa and transduce the apoptotic signal in EPCs. Secondly, having recently established a B19V culture system that mimics native B19V infection of human EPCs in bone marrow under hypoxic conditions, we will carry out high throughput screening (HTS) of a library of small molecules (available at the University of Kansas HTS Core Laboratory; contains over 100,000 druglike small compounds) for anti-B19V infection drug candidates. The B19V culture system can generate virus in sufficient quantity for such screening, and the cell death marker can be readily applied to assess B19V infection as a readout. We will use a cell-based luminescent cytotoxicity assay to screen the library. Because B19V vaccine is currently unavailable, and immunocompromised patients would be unable to respond to a vaccine, there are currently no viable treatment options for diminishing the bone marrow failure caused by B19V infection in patients with acute or persistent B19V infection. The study proposed in this application is expected to identify targets for the development of drugs capable of eliminating B19V from human EPCs, and this will ultimately lead to diminished bone marrow failures in these patients. In addition, our analysis of the mechanism underlying apoptosis of EPCs is expected to reveal pathways that may be involved in erythropoiesis or the disruption of erythropoiesis under certain disease conditions.